The present invention relates to a rubber composition that, in its vulcanized state, may be used in a safety support intended to be mounted on a wheel rim within a tire. The invention is also directed to the safety support, which is capable of supporting a tread of the tire in the event of a drop in inflation pressure and to a mounted assembly comprising the support.
Safety supports for vehicle tires are intended to be mounted on a rim within the tire for the purpose of supporting the tread of the tire in the event of a loss of inflation pressure. Such supports comprise a base which is intended to conform to the rim and a crown which is intended to come into contact with the tread in the event of loss of inflation pressure, but leaves a clearance relative thereto at nominal pressure.
Japanese patent specification JP-A-3/82601 discloses a safety support comprising a substantially cylindrical base and crown, which further comprises an annular body connecting the base and crown.
This annular body comprises a supporting element which is continuous circumferentially having:
a plurality of partitions extending axially on each side of a circumferential median plane and distributed around the circumference of the support, and
joining elements extending substantially circumferentially, each joining element connecting the respective ends of two adjacent partitions which are arranged on the same side of the support, said joining elements being arranged alternately in succession on each side of said partitions;
in which the partitions and joining elements are substantially rectilinear and the difference between the maximum and minimum values of the area of an axial section of the support element as a function of the azimuth, relative to the sum of these same areas, is preferably less than 0.3. As a consequence, as a function of the azimuth, the area of an axial section of the support element varies at most by a factor of two in order to ensure good uniformity of loading capacity and to limit vibration when running on the support.
This support is produced from a hard polymeric material, with the whole supporting element being designed to withstand compressive loads.
Such supports may be produced in conventional manner, for example by injection molding.
Vulcanized rubber compositions intended to constitute part of a tire and which exhibit improved rigidity characteristics are also known; See, e.g., U.S. Pat. No. 5,023,301 which discloses compositions that comprise an elastomer matrix in which polypropylene fibrils of a maximum length of 15 xcexcm and a reinforcing filler are randomly dispersed.
One major disadvantage of the composition is its reduced elongation at break in comparison with a xe2x80x9ccontrolxe2x80x9d composition not containing polypropylene fibrils (the ultimate elongation modulus is less than one third of the corresponding modulus of the xe2x80x9ccontrolxe2x80x9d composition). Such compositions, therefore, are not suitable for constituting safety supports.
The object of the present invention is to provide a rubber composition, which in its vulcanized state can be used in a safety support intended to be mounted on a wheel rim inside a tire. The composition is such that it provides for improved weight reduction performance for the support over known supports at a comparable flat running service life.
The rubber composition according to the invention comprises (in parts by weight per 100 parts of diene elastomer(s)):
at least one diene elastomer,
particles of an xcex1-olefinic thermoplastic polymer, having a melting point greater than or equal to 150xc2x0 C., in an amount of from 5 to 30 phr, wherein the mean particle size by weight of particles is between 30 xcexcm and 500 xcexcm,
more than 60 phr of a reinforcing filler and
from 3 to 8 phr of sulphur.
Both the non-vulcanized and the vulcanized rubber compositions are contemplated in the present invention.